Students can navigate to their Progress Tab and select the previous term using the term selector in the upper right of the Course heading

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The student's cannot view 2 terms at the same time so they should be sure to deselect the current term if they are looking for past term's assignment grades.  

At this time, Parents do not have the same functionality.  Parents should select the child they wish to view and select the Assignments tab.  From here they can click the reports icon in the upper right and select and run the View Assignment Grades w/comments report.  

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Here they will be able to select the term they would like to see grades for and run the report.